1999 Chevrolet Cavalier car wont start

If it cranks good but won't start, have a helper crank it, while you visually check for spark at the spark plugs. If spark everywhere, use a gage and check fuel pressure. I realize on some makes and models checking for spark and fuel pressure can be a pain, but, still necessary.

The back firing could be a valve timing issue?

Was the ignition module tested off the vehicle? If so, the system needs to be tested on the vehicle, for spark. What if the primary wiring for the module has a problem? No spark.

You said you tried ether, any reaction? You need to visually check for spark at the plugs. Use a gage and check fuel pressure, also check for fuel injector pulse, all with engine cranking.

Can you check applicable trouble codes? To check codes, yourself, at the least, you need an obd2 code reader.

You should have a timing chain. If good fuel and spark, but no cylinder compression, it won't start. If the cranking rpms are faster than normal, then definitely check compression.

If you have been cranking the vehicle a bunch, make sure the battery has a full charge.